LINCOLN COUNTY, Mo. (KMOV) – New details have emerged after 17-year-old Blain Michael Erp was charged Thursday for allegedly threatening to shoot up Troy Buchanan High School.

Thursday evening, more information surfaced describing the events leading up to that incident.

According to court documents, Erp's girlfriend told authorites she had several arguments with him during the week, during which he had threatened certain students. She provided a list of four students that she felt could potentially be in danger.

Erp's girlfriend said he was mad at these students mostly for having contact with her.

Additionally, she told authorities that Erp had specific plans for how he would carry out his attack. She said he told her he planned to use a pistol to shoot the four students listed, then use an assault rifle to kill all of the students in his gym class that he felt were mean to him.

His girlfriend said he showed her three loaded handguns and an assault rifle he planned to use in the shooting. She also said he had a firearm on him when he picked her up at Jack in the Box restaurant on Monday.

In her statement, Erp's girlfriend said he was heavily involved in synthetic drug use, and she had seen him hurt himself on several occasions because he "liked the pain."

In another statement made to authorities, one of Erp's best friends confirmed the drug use, saying Erp used synthetic drugs "every other day at least."

Court documents show the best friend told police Erp had discussed the Columbine High School shooting with him a week earlier.

The friend said Erp often bottled up his anger and would explode when he was provoked. He also claimed Erp had threatened to kill his girlfriend if she "continued to push him."

The threat forced police to place Troy Buchanan High School, Troy Middle School and New Horizons High School under a lockdown.

According to authorities, Erp threatened to kill his family before opening fire at the school.

They eventually reached Erp by phone and told him to turn himself in. He was later taken into custody near the Lincoln County Sheriff’s Office.